1. Field of the Invention
The present invention relates to a pattern generation system and, more particularly, to a pattern generation system for raster-scanning a laser beam on a workpiece to perform automatic drawing on the basis of design pattern data.
2. Related Background Art
Various types of conventional laser pattern generation system have been proposed. According to this system, a photoresist or dry film formed on a workpiece is scanned with a laser beam optically modulated on the basis of design pattern data, thereby forming a micropattern with high precision.
In order to form patterns on two-sided circuit boards, multilayer circuit boards, or film substrates, each board or substrate is subjected to repetitive pattern formation. During repetition of operations, patterns on the upper and lower surfaces of each two-sided circuit board and wiring patterns of the respective layers of each multilayer circuit board must be drawn with high precision.
If dimensional errors occur, positional errors occur in electrode positions of the upper and lower surfaces of the two-sided circuit board and wiring patterns of the respective layers of the multilayer circuit board. In the subsequent through hole formation process, electrodes to be connected to each other are then often disconnected and are erroneously connected to other conductive patterns to be electrically isolated from the electrodes. In addition, since a sufficient dimensional margin is not guaranteed, incomplete insulation may occur.
The dimensional errors are not only caused by drawing errors with a laser pattern but also mounting errors upon mounting of a substrate or board on a work table, and expansion/shrinkage of the board or substrate in intermediate treatments (e.g., heat and chemical treatments) performed during the repetitive exposure operation.
In order to prevent the substrate or board mounting error, fiducial points or lines are marked on a substrate and a table to locate the substrate at a predetermined position. More specifically, a plurality of pins extend on the table so as to respectively correspond to a plurality of through holes formed at predetermined positions of the substrate, thereby positioning the substrate in the accurate location.
However, in practice, if the substrate expands or shrinks, the pitches of the through holes are changed. In addition, since margins are provided for the through holes or the pins, it is difficult to perform accurate positioning. In practice, a substrate deformation amount during the intermediate treatments is manually measured, and a scanning distance along the X direction and the displacement of the table along the Y direction are finely adjusted to correct expansion/shrinkage at the time of pattern drawing.
The method of manually measuring the deformation amount requires cumbersome and time-consuming operations. In addition, correction errors caused by measurement errors are still involved.